General Embodiment 1
Ultraviolet radiation is composed of three ranges, namely: UVA, which is from 320 to 400 nanometers, UVB which is from which is from 280 to 320 nanometers, and UVC which is from 100 to 280 nanometers. UVA and UVB are attenuated by the atmosphere, but is still reaches the earth""s surface. UVC is usually blocked by the ozone in the atmosphere. Man-made lighting sources also produce ultraviolet radiation. Most fluorescent lighting has a high output in the UVA range. UVB causes more damage than UVA, but all ultraviolet radiation will cause degradation to materials.
Ultraviolet rays from the sun, or from man-made sources, degrade many materials by breaking their molecular bonds. Dyes and inks fade from ultraviolet, plastics lose their properties, paints chalk and fade, and many other items are damaged. Strategies to combat ultraviolet degradation include the use of materials that absorb ultraviolet radiation and convert it to heat energy. Most absorbers have an ultraviolet cutoff of 365 nanometers. A few have higher cutoffs, up to 384 nanometers with little to no yellowing. The phenomenon of producing a yellow cast when absorbers are used to block all of the ultraviolet radiation is due to the gradual slope of the absorption curve of the absorbing material. This slope, when the cutoff is extended to 400 nanometers, causes absorption of violet and blue light. The absence of blue light is perceived as yellow, and it is for this reason that most absorbers, especially in clear overcoatings, are not used to block all of the ultraviolet radiation up to 400 nm.
The optical density of a filter, an absorber, or a coating, to a range of radiation, is directly related to the concentration and thickness of the layer. The thinner the layer, the light the concentration of absorber is required. Very thin coating layers, below 10 microns cannot contain sufficient levels of absorption without a significant loss in the properties of the coating material. As an example, a 4 micron clear coating might require thirty percent, by weight, of an absorber to have complete absorption up to the cutoff wavelength of the absorber. Some common classes of ultraviolet absorbers are benzophenones and benzotriazoles.
A coating layer that is effective in blocking ultraviolet and is thin has the additional advantage of lower material cost and a higher degree of possible flexibility. A coating with a log concentration of absorber, so that the physical properties of the coating layer are not diminished, as well as the lower cost of using less absorber, that blocks all ultraviolet up to 400 nm, and does not have a significant effect on blue light absorption would a significant improvement in the effort to stop ultraviolet damage to materials.
The disclosed coating system blocks ultraviolet radiation up to and including 400 nanometers, the upper end of the ultra violet light. Preventing ultraviolet (uv) radiation from reaching materials and surfaces greatly improves weatherability and resistance to physical degradation from the effects of UV radiation on chemical bonds. There currently exist many types of ultra violet inhibitors, which are meant to be included in materials to improve their resistance to uv radiation. The damage from uv radiation is greater as the wave lengths of uv become shorter. However, considerable damage still occurs from the longer wavelengths of uv radiation. It is desirable to block the uv radiation and not have yellowing effect. The disclosed coating system remains water white.
In accordance with the invention, the disclosed coating system is a two-layered system using a typical ultraviolet absorber in its inner layer (called the blocking layer), furthest away from the source of ultraviolet exposure, with a fluorescent material with reflects ultraviolet radiation back as blue light. The ultraviolet absorber in the inner layer is used in sufficient concentration to have an ultraviolet cutoff, which can be extended with the fluorescent material. There are natural fluorescent materials such as calcite, will mite, sprite, fluorite, and diamonds. Three are also man-made fluorescent materials used to make materials look whiter by reflecting the long wave ultraviolet radiation as blue light. These are called optical brighteners. Typical optical brighteners are disulphonates, tetrasulphonates, and hexasulphonates. These are water soluble optical brighteners. An example of a solvent soluble optical brightener is Uvitex OB from Ciba-Geigy Corp. Such optical brighteners are typically used in textiles at very low concentrations of less than one percent by weight. Their purpose is to reduce the yellowness of a material, dye, plastic, etc. The present invention provides the desired protection by combining an optical brightener with an ultraviolet radiation absorber which raises the cutoff wavelength and increases blue light, rather than absorbing blue light as a longer wavelength cutoff ultraviolet absorber would normally do.
This barrier require high levels of optical brightener to convert the longer wavelength ultraviolet radiation into blue light and do this effectively enough to block the transmission from outer layer to the inner layer due to the total conversion of longer wavelength ultraviolet to blue light. The high level of optical brightener causes a significant fluorescent effect upon exposure to ultraviolet radiation, where this layer will glow with blue light.
The Surface of the inner or blocking layer also has a significant quantity of fluorescent material, which is not protected in depth by the included ultraviolet absorber. This is the primary reason the second or outer coating layer is effective in reducing fluorescence and why it is necessary. The fluorescent material in the inner layer that lies in the matrix of resin and ultraviolet absorber is then protected from excessive fluorescent excitation. Another technique is to use an alkaline material in the outer coating to decompose the surface of the optical brightener of the blocking layer. Still another technique to reduce surface fluorescence is to use an optical brightener quencher such as OBA Quencher from Kalamazoo Paper Chemicals Corp.
While a single blocking layer can be used for protection against ultraviolet, the fluorescent blue glow is generally undesirable. In order to significantly reduce this fluorescence, it is necessary to reduce the amount of ultraviolet that reduces this layer in the peak wavelengths for fluorescence. This is done by applying an overcoating to the blocking layer, which contains some level of ultraviolet absorber that reduces the ultraviolet transmission of the wavelengths that cause fluorescence. It is then this combined effect and balance, which completely blocks ultraviolet radiation without yellowing.
The outer coating can provide other properties such as chemical resistance, scratch resistance, slip, or friction. The outer coating material can be any resin system with an ultraviolet inhibitor, but it is preferable clear and relatively ultraviolet transparent. Materials that do not absorb ultraviolet on their own are relatively unaffected by exposure to it. For this reason, typical clear outer coating resins would be aliphatic urethanes, polysiloxanes or acrylics.
Fluorescent materials have been used in may applications to xe2x80x9cwhitenxe2x80x9d whites, or brighten colors in may products. The teclunique is to use the fluorescent material to increase the reflected blue light. The increase in blue light is perceived as a reduction in yellow light form the fluorescent material. It typically takes very small quantities of fluorescent material to accomplish this brightening effect.
UV absorbers are widely available and are commonly used with intention of blocking primarily UVB. When these uv absorbers are used to block all uv light, they increase yellow light perception due to the reduction in blue light.
Higher concentrations of fluorescent materials in a single layer coating will cause a blue fluorescent glow to the material when it is exposed to uv light. This is cosmetically objectionable. For this reason, only low concentrations are used for brightening.
Blocking uv from reaching the surface of an object is a function of film thickness and concentration. Thin films down to 3-5 microns would require very high concentrations of uv absorbers to have complete blocking power. These thin films, such as those in polysiloxane abrasion resistant coatings, would need uv absorber concentrations as high as 30 percent to accomplish an optimal absorption based on the uv absorber. At that concentration, the properties of the coating are drastically degraded.
The inside layer of the present system can be in a range of 6 microns or higher, using Uvitex OB (Ciba-Geigy), with 9-15 microns being optimum. This range is based on the maximum solubility of the uv absorber and the fluorescent material. If other uv absorbers and fluorescent materials are chosen, this film thickness range can be adjusted accordingly.
The second or outer coat, in order to maintain flexibility, must be in the 3 micron-3 mil range film thickness depending on the brittleness of the resin system. In order to maintain the properties of the outer coat at this film thickness, it is necessary to keep the uv absorber in this layer at the maximum level before degradation of the physical properties of the coating occurs.
In accordance with the invention, the disclosed system includes an outer coating which also has a uv absorber to prevent the blue glow at the inner surface of an inner layer. This blue glow will appear hazy prior to application of the outer coating.
UVA absorbers that block all uv up to 400 nm tend to be significantly yellow in color. This is because of their absorption curve. The more gradual the slope of the curve the more visible blue and violet light is absorbed which is then perceived as yellow. It is desirable when blocking uv up to 400 nm to have a very steep transmission curve with a transmission cutoff at 400 nm to avoid the yellowing effect.
Degradation due to outdoor exposure also occurs from pollutants, which are carried to the item via precipitation and air. These pollutants are typically oxides and various dilute acids such as acid rain. The pollutants can cause colorants to fade, as the molecular bonds are broken. It is desirable to have protection against this type of chemical breakdown such as a chemically resistant barrier.
Certain items, such as printed paper, can also be damaged by precipitation such as rain and snow, which, in the form of water, causes the paper to deteriorate and some print materials such as ink to bleed. It is therefore desirable to create a barrier to precipitation for good outdoor weatherability.
There currently exist coatings and laminations, which are partial uv blockers and which are transparent but have poor abrasion resistance, such as vinyl coatings and laminates. It is desirable to have good abrasion resistance in a product to be used outdoors to prevent changes in gloss levels from abrasion which might be caused by windbome debris or cleaning.
The current practice of including uv absorbers in the body of plastic items or in overcoatings is often of limited effectiveness because it is weakened by the relationship of film thickness and concentration of uv absorber. The thicker the coating the lower the concentration of uv blocker necessary. Thin coatings are often desirable due to cost and flexibility. When a uv absorber is included in a colored molded item, the surface has the lowest concentration of uv absorber and so this surface degrades quicker than the material behind this surface. Thus, even though the colored material contains uv absorber, its relative concentration at the surface of the item is low, so the color fades at the surface. With suitable coating, the weatherability of a molded plastic item is improved in terms of physical properties except for a significant improvement in color fade, as this is a surface effect. The bulk of the material has protection in depth.
The best combination of protection against color fade is to include pigments, which are resistant to uv degradation along with uv inhibitors. In the inkjet industry it is common to combine uv resistant inks with an uv inhibiting outer laminate for further Protection against fading in applications where long term exposure to uv is expected.
Solvent selection requires compatibility with the resin systems and additives, leveling characteristics, and the prevention of crystallization of the additives. The following examples are illustrative.
The following example achieves a 9-10 micron film thickness. Percentages are by weight of volume solids.
The best order for mixing is to determine the amount of toluene that will be the diluent and stir in the Tinuvin OB until it completely dissolves. Add the uv inhibitor and stir until completely dissolved. Add the Desmophen 670-80A and stir until completely dissolved. Add the dibutyltindilaurate and stir. Add the catalyst and stir gently, until it is completely dissolved. The solids level of this coating can be adjusted to the processing technique and conditions to achieve approximately 15 microns film thickness. The lower the film thickness, the higher the required level of Tinuvin 328 and Tinuvin OB. The ratio between uv inhibitor and fluorescent material is dependent on the uv absorption of the inhibitor and the wavelength shift of the fluorescent material. The goal is to make the uv cut-off up to 400 nm and then have maximum light transmission for the visible spectrum.
The outer coatings provide desired physical properties and they provide quenching of the optical brightener at the surface of the inside coating. This quenching is accomplished by uv transmission reduction by the outer coating an/or by adding a higher pH material, such as minor amounts of tetramethylaminohydroxine to the outer coating which quenches the optical brightener.
Some typical applications are store front display windows to protect the items on display from ultraviolet damage, protection of inkjet prints which are very susceptible to ultraviolet degradation plastic sheeting which degrades and turns yellow in outdoor applications, works of art which are subject to man-made ultraviolet radiation, and, in general, any item that is damaged by ultraviolet radiation. In order to achieve weatherability of inkjet prints which may be used for signs, posters, billboards, etc., it is often necessary to laminate them with films that provide protection against ultraviolet radiation.
In another embodiment, a thin layer of polyester film is coated on one surface with the blocking layer and the second coating is applied to the opposite surface. The film is provided with a suitable laminating adhesive, such as heat-activated vinyl, EVA, and similar adhesives. The film may be applied to an inkjet print on the printed side. This embodiment of the coating systems forms a thin flexible transparent tear resistant laminate which blocks out ultraviolet to less than one percent transmission at 400 nm and to less than 0.1% transmission below 400 nm down to 280 nm. A polysiloxane coating also provides scratch resistance, as well as chemical resistance.
By providing a two-layer system, rather than a single layer system, It is possible to have the inner layer absorb the bulk of received ultraviolet radiation, and reflect radiation above 375 nm as blue light, so that the coating is seen as clear rather than as a yellow tint. Most conveniently, both layers are applied using known spraying techniques in serial fashion, which lends itself to the application of both layers upon a thin polyester film, and the like. Other methods are possible, including dipping, flow-coating, curtain coating or by any other liquid application method. I wish it to be understood that I do not consider the invention to be limited to the precise detains and examples described hereinabove, for obvious modifications will occur to those skilled in the art to which the invention pertains.
General Embodiment 2
This invention relates generally to the field of light blocking or light absorbing filters, and more particularly to an improved filter material suitable for blocking harmful ultraviolet rays from artificial light transmitting sources.
It is known in the art to provide ultraviolet light blocking filters which are in the form of coatable fluids, or laminated sheets of clear synthetic resinous materials which are applied directly to an article to be protected to improve the resistance fading and other deterioration caused by exposure to daylight, and in particular, sunlight. Radiation in the ultraviolet spectrum and particularly that in the range of 365 nm and 400 nm is particularly destructive. However, most widely used filtering materials are effective up to about 365 nm, but are of drastically reduced effectiveness above that value.
Many valuable, indeed, irreplaceable objects are exhibited in museums, which for the most part are illuminated by artificial light of both fluorescent and incandescent types. For the most part, such lighting does not provide a serious problem. Such museums are, however, visited by millions of viewers each year, many of whom take their own photographs using electronic flash units which transmit light of a quality having sufficient ultraviolet wave lengths including the above mentioned upper range. While a single exposure produces negligible amounts of ultraviolet light, where even a small fraction of the visitors photograph the same objects, the cumulative effect of such exposure is substantial. As a result, many museums, forbid the taking of photographs by visitors altogether.
Because electronic flash illumination is normally transmitted through a focusing lens, it has not been heretofore possible to filter this light as a practical matter.
Briefly stated, the invention contemplates the provision of a novel ultraviolet filter material capable of full ultraviolet wave blockage in coatable fluid form which may be readily permanently adhered to transparent glass or plastic surfaces, and which will not interfere with the transmission of visible and photoactinic energy. This material is applied preferably to the inner surfaces of electronic photo flash lamps or focusing lens therefor, and may also be used in the manufacture of any light source in which the elimination of ultraviolet light is desirable. Most suitably, the composition is applied in thickness ranging from five to ten microns using standard application techniques, such as flow coating, spray coating, dipping, curtain coating and the like. It may also be used with coating thicknesses of as little as 2 microns, with the use of certain precautions.
It is a principal object of the present invention to provide a coating which can be applied to the lens or envelope of a light source, or a window which is transmitting light, that will be waterwhite, and efficiently block ultraviolet emission employing coating thickness of less than 50 microns, typically less than 10 microns. It is also an object of this invention to block ultraviolet transmission from light sources which typically also emit heat. This aspect is important with regard to any resin system thermally degrading and yellowing or cracking.
Sources or lenses covering light sources can be coated with resin systems that are themselves, for the most part, transparent to ultraviolet transmission, and so unaffected by it, and that contain ultraviolet inhibitors or other ultraviolet reducing materials such as fluorescent materials which will efficiently block ultraviolet transmission. These coatings can be applied to laminating films which can be applied to flat surfaces, or to laminating films which can be thermal formed over curved surfaces.
Certain of the disclosed embodiments are not only capable of blocking ultraviolet light, but actually converting at least a portion of the ultraviolet light to visible light, thus increasing the efficiency of light transmission which is particularly useful when the covering is applied to an incandescent or fluorescent light source. This effect is obtained by the incorporation of a fluorescent material in larger quantity as compared to the material used for ultraviolet absorption.
There are several commonly available systems that are essentially ultraviolet transparent and therefore unaffected by ultraviolet exposure. These include acrylics, urethanes, polysiloxanes, and to a lesser degree, phenoxy resins.
The two main classes of ultraviolet inhibitors are benzotriazoles and benzophenones. The benzophenone class tends to be very yellow when used in concentrations that efficiently block ultraviolet transmission. The benzotriazoles typically block ultraviolet transmission up to 365 nm and a few of them will block ultraviolet radiation up to 380 nm.
Including a fluorescent material that converts long wavelength ultraviolet into longer wavelength blue light will increase the ultraviolet blocking efficiency up to 400 nm. The inclusion of fluorescent material may not be necessary if the light source is a man-made light source which does not emit the longer wavelengths of ultraviolet light.
The phenoxy resin systems can be cross-linked with typical cross linkers for hydroxy-functional resins, such as melamine, urea-formaldehyde, heat reactive phenolica, and isocyanate-flnctional prepolymers.
Dipping, spraying, flow coating, curtain coating, or any other liquid coating application technique can apply these coatings. The following examples are illustrated. Proportions are by weight of resin solids.
To improve adhesion to glass surfaces requires heating to 350 F. for ten minutes or longer times at lower temperatures. In some cases, the heat of an incandescent light source will be sufficient to fully crosslink this coating.
Using acrylic solids, the following formulation is suitable; proportions are by volume of resin solids.
To improve adhesion to glass surfaces, it may be necessary to pretreat the glass surface by etching or treating it with a hydrolyzed amino silane coupling agent, or to other commonly known techniques to provide good adhesion to glass.
The Uvitex OB may be omitted if complete ultraviolet absorption is not required. Using the Tinuvin 328 alone at the described concentration to resin solids will produce an ultraviolet cut-off at 380-384 nm at a 9-micron film thickness.
These coatings may be further protected by overcoatings for additional chemical resistance or abrasion resistance. Some examples are aliphatic urethanes and polysiloxanes.
The described embodiments relate to a thin coating that can be applied to either the inside surface of, or the outside surface of light sources or display window. As discussed above, ultraviolet light is the primary cause of photo degradation of may exposed items. It is the primary cause of colors fading, paints chalking, paintings cracking, fabrics fading, and the loss of physical properties such as tensile and impact strength of many materials. Ultraviolet is defined as light having a wavelength of 400 nm or less.
The current technology reduces the photodegradation effect of ultraviolet light by including ultraviolet inhibitors in the body of materials to be protected or by overcoating the products with ultraviolet resin systems. Most ultraviolet inhibitors block or absorb ultraviolet radiation up to 380 nm in coatings that are at least one nm thick. Thinner films usually absorb considerably less ultraviolet not only in optical density, which is the percentage absorbed, but also not as high at 380 nm. The most common absorption cut off is 360 nm.
Articles formed from materials that have ultraviolet inhibitors included still have photodegradation at the surface. Absorption efficiency is determined by the absorption characteristics of the inhibitor and is directly related to concentration and thickness. The thinner the film, the higher the required percentage of ultraviolet absorption material required. For example, a 9 micron film may require 30% based on resin solids for efficient blocking. Most ultraviolet inhibitors will impair transparency when included in clear coatings at that level or they will degrade the physical properties of the coating resin system.
An example of an application is light sources in museums. Museums are very cautious about picture taking and light source relative to artwork or artifacts. All incandescent light sources emit ultraviolet radiation, as do all fluorescent light sources. Coating the surface of the emitting source with a total ultraviolet blocking coating protects all items exposed to that source. Electronic flashes are normally provided with a focusing lens which can be coated to completely block ultraviolet thus making them safe in museum and art galleries. Preferably, this coating is done on the inner surface of such lenses.
1. Paphen phenoxy resin PKHC range 10%-40% (Phenoxy Specialties, Rock Hill, S.C.)
2. Cymel 303 melamine resinxe2x80x94range 2%-10% (Cytec Industries, Long Beach, N.Y.)
3. P-toluene sulfuric acid catalystxe2x80x94range 0.001-%-0.1%
4. Uvitex OBxe2x80x94range 1%-6% (Ciba-Geigy) Optical brightener
5. Tinuvin 328xe2x80x94range 0.2%-4% (Ciba-Geigy) U.V. absorber
6. Solvents for dilution to create the desired film thickness, including methyl ethyl ketone, dioxolane, toluene and others to make 100%.
The above formulation has excellent tensile strength. These properties are of particular value when the coating is applied to a glass light bulb. The coated bulb will tend to be held together when the bulb is broken, for improved safety.
Cymel 303 solidsxe2x80x94range 20%-50% (Cytec Industries)
P-toluene sulfuic acid catalystxe2x80x94range 0.01%-0.3%
Uvitex OBxe2x80x94range 1%-8% (Ciba-Geigy)
Tinuvin 328xe2x80x94range 0.1%-4% (Ciba-Geigy)
Solvents for dilution to achieve film thickness, including toluene, xylene, methyl ethyl ketone, dioxolane and others to make 100%.
Either sample will cure at temperatures of 250 F. -350 F., with shorter times for higher temperatures.
The primary material that blocks most of the ultraviolet light and converts it to visible light is the Uvitex OB in sufficient quantities ranging from 0.1% to as much as 8%. As indicated by the following graph, this light appears as visible light in the range of 420 nm to 575 nm, with peaks at 440 nm and 490 nm. This result was obtained by coating a standard 20 watt fluorescent tube to 9 nm thickness. It has been determined that in the case of incandescent and fluorescent lamps, the covered ultraviolet light may range to as much as 30 percent to 50 percent of the total light output.
Absorption of ultraviolet radiation up to 380 nm employs a standard ultraviolet absorber. Absorbing up to 380 nm is not a requirement. It may be less than 340 nm provided that the fluorescent material makes up the difference. The fluorescent material converts ultraviolet radiation from about 340 to 400 nm to visible light. This provides a complete ultraviolet cutoff with almost any commercially available ultraviolet absorber combined with a fluorescent material.
If intense ultraviolet radiation reaches the disclosed blocking system, it may cause a glow from the fluorescent material. However, two steps can prevent the glow using a two-layer coating system, and using a slower drying solvent such as acetylacetone, or similar solvents such as xylene. A requirement is that the solvent dry slowly, and must be compatible with the resin system, the ultraviolet absorber, and the fluorescent material.
This can also be accomplished in a single solvent system as thin as 2 microns. The lower film thickness is provided by increasing the percentage of ultraviolet blocking materials to 40 percent based on resin solids. This is useful, for example, in dye transfer sublimation, where low film thicknesses are absolutely necessary to transfer the coating from a film to the surface of an image.
If the film thickness is increased to 9 microns, the level of ultraviolet blocking materials is decrease to 19 percent based on resin solids.
High temperature resin systems can be used with the disclosed system for application to high temperature light sources. Another embodiment is to provide a hybrid lightbulb, one that is coated with a fluorescent material on its outside surface to convert the ultraviolet emission of the bulb in to visible light. No ultraviolet absorber is necessary unless it is necessary to remove the ultraviolet radiation below 340 nm. The object of this embodiment is to increase visible light by converting ultraviolet light into visible light. A side effect is that the conversion also blocks the ultraviolet from about 340 nm and higher. If it is also necessary to block lower ultraviolet wavelengths, then an ultraviolet absorber must be used with the fluorescent material.
Each of these coatings uses a binder resin. The properties of the binder resin allow these coatings to be use din different applications. For example, the bulb coating can be made with a fluorescent material and a high temperature resin such as GR 150 or GR 908 (polysiloxane resin, from Techneglas). These resins can withstand very high temperatures for extended periods of time. These resins can also be used on high intensity halogen bulbs, which have a very high ultraviolet emission. For low temperature applications, such as a fluorescent bulb, acrylic resin can be used. IN such applications, it is not a requirement to use an ultraviolet absorber in the lightbulb coating, merely a fluorescent material.
The concentration of fluorescent material is optimized in the following example:
GR 150 (Techneglas, Long Beach, N.Y.) at 15% solids
MIBK/Toluene 50150% we weight
Acetylacetone 8% of total weight
Uvitex OB 19% based upon GR 150 solids
BYK 330 (BYK Chemie, Middletown, Conn.) 0.5% based on resin solids
Using the proportions of Example 6, GR 150 is substituted by G.R. 908 (Techneglas).
It will be appreciated that a variety of ultraviolet absorbing materials may be used in conjunction with an optical brightener which will be operative to cover the range commencing t the wavelength where the ultraviolet absorber ceases to operate, to provide a substantially complete cutoff.
the relative output of a coating versus an uncoated 20 watt fluorescent tube. In the case of the uncoated lamp, radiation commences at about 330 nm, with the bulk of the light put output extending between that point and 425 xcexcm. There are peak outputs at 440 nm, 550 nm, and 575 nm.
By contrast, the coated lamp has substantially all radiation up to about 415 nm completely blocked, with the visible output commencing at about 420 nm and extending 30 to about 570 nm. It will be observed that there is an area commencing at 425 nm where the curve crosses and extends above that for the uncoated lamp to about 570 run, indicating that a portion of the ultraviolet light has been converted to the visible light spectrum.
I wish it to be understood that I do not consider the invention to be limited to the precise details disclosed in the specification, for obvious modifications will occur to those skilled in the art to which the invention pertains.
General Embodiment 3
The ultraviolet block material of the present invention, has transmittance of the light within a range of wavelength of 300-380 nm of 10% or less, preferably transmittance of the light within a range of wavelength of 300-390 nm of 10% or less and, particularly preferably, transmittance of the light within a range of 300-400 nm of 10% or less while it has a transmittance of the light within a range of 420-800 nm wavelength of 90% or more or, preferably, 95% or more.
Especially when the transmittance of ultraviolet light within a range of 350-380 nm wavelength, preferably 350-390 nm or, particularly preferably, 350-400 nm wavelength is too high, such ultraviolet light decomposes the colorant whereby it is not possible to effectively prevent color fading, discoloration and decolorization.
When the transmittance of light within a range of 420-800 nm is too low, the ultraviolet block material is colored or the transparency thereof is lowered disadvantageously.